1. Field of the Invention
The invention in general relates to the ultrasonic testing of materials, and particularly for the detection of discontinuities extremely close to the surface of the material being tested.
2. Description of the Prior Art
Various ultrasonic techinques are widely used for the detection of flaws in materials such as metal stock or finished parts. Basically, an ultrasonic transducer projects a pulse of acoustic energy into the workpiece under test and any discontinuity or flaw within the workpiece will reflect the projected acoustic pulse. This reflected pulse may then be detected by the same or a separate transducer to thereby give an indication of the presence and depth of the discontinuity.
In some systems a plurality of transducers are utilized for projection and reception of acoustic pulses together with computer analysis of the reflected wave forms so as to obtain more information regarding not only the depth but the size and orientation of the discontinuity.
With these systems, the limits on resolution with, for example steel-based alloys, generally approach approximately 50 mils (1.27 mm). That is, these systems are not able to detect flaws within a few mils of the surface.
A need, therefore, exists for an arrangement which can detect these near-surface flaws and the present invention is operable for detecting some of these flaws.